Magnetic transducer assembly support structure



APril 23, 1968 w. H. LIGGETT ETAL 3,380,041

MAGNETIC TRANSDUCER ASSEMBLY SUPPORT STRUCTURE Filed April 1. 1964 2 Sheets-Sheet 1 I i a Avmvmec M04444 1/66572 ,4; WA 1. Ina/ 4 Mme April 23, 1968 w. H. LIGGETT ETAL 3,380,041

MAGNETIC TRANSDUCER ASSEMBLY SUPPORT STRUCTURE 2 Sheets-Sheet 2 Filed April 1, 1964 r 4, M A. M 4 M 4; l /A A firm/{4 5v Mam A 24/ United States Patent ABSTRACT OF THE DISCLOSURE An electromagnetic transducer assembly is rigidly supported in and by a fixed structure of an information storage device. The assembly and structure are closely spaced from a rotating drum having magnetically sensitive material for storage of information. The support structure includes a plurality of cylindrical bores which extend from the outer periphery of the structure to substantially the inner periphery of the structure to provide a flat end wall. A rectangular opening in the end wall opens the bores to the interior of the support structure. The transducer assembly has a core which has a pair of steps at the pole pieces thereof and these steps are adapted to contact the end wall of the structure when the transducer is placed within the bore. The pole pieces of the transducer will then extend through the opening in the end wall so that it will be closely spaced from the magnetic sensitive surface. The transducer assembly also includes a material which has a thermal coefiicient of expansion which is substantially similar to the thermal coeflicient of expansion of the material of the support structure so that any change of temperature will not vary the distance by which the transducer pole piece extends within the opening in the end wall.

The present invention relates to information storage devices and more particularly to a magnetic drum information storage device having the rotatable magnetic storage drum as its only moving element.

In general, the term information storage relates to a process whereby information, such as electrical signals representative of discrete bits of information, typically of an analogue or digital form, are stored in a magnetic medium by means of an electromagnetic transducer. The number of bits of information which may be stored per linear inch of recording surface is limited, among other factors, by the spacing of the pole pieces of the electromagnetic transducer from the recording surface of the magnetic medium. Generally, the pole pieces include a common pole face surface having a gap transversing its width to separate the pole pieces so that the magnetic flux lines are set up between the pole pieces across the gap and encounter the recording surface to magnetize a predetermined portion. Thus the smaller the gap the better the magnetic coupling, and the less the flux spreading. Typically flux spreading is the magnetization of a greater than desired portion of the recording surface by the lines of flux which fringe between the two pole pieces. In magnetic data storage systems where the wavelength of the recorded information measured along the recording medium is relatively short, for example, high density digital storage systems having information storage ca pacity in the order of 500 bits per linear inch minimum flux spreading is achieved by maintaining a gap width in the order of 280 microinches.

In the past, many mechanical configurations of electromagnetic transducer and magnetic mediums have been attempted with varying degrees of success. The first, and perhaps most undesirable configuration for high density storage systems might be called contact recording since the pole face surfaces of the electromagnetic transducer are maintained in uninterrupted contact with the recording surface of the magnetic medium. While this configuration eliminates flux spreading inherent in the separation of the surfaces, it increases the problem of damage due to abrasion, chipping, and scoring of the pole face surfaces and the magnetic recording surface. Therefore, to minimize these problems, a second configuration might be called out of contact recording because the pole face surfaces are physically separated from the magnetic me dium or recording surface by a precise accurately maintained gap. The mechanical problems of designing a support structure and the mounting of an electromagnetic transducer thereto so that during operation the pole face surfaces are maintained at a precise distance from the recording surface is staggering and the cost is prohibitive since temperature changes may account for a variation in the spacing of more than the desired width of the gap.

To efficiently and commercially achieve the desired gap, considerable Work has been done to develop systems wherein an extremely thin layer of hydrodynamic or hydrostatic lubrication is used. One such system biases the pole face pieces into contact with the surface of the magnetic medium and maintains this contact during relative later-a1 motion of the surfaces until the resultant hydrodynamic eifect develops a component of force which balances the biasing force at a predetermined constant spac ing of the surface.

In another system air is blown against the recording surface through a nozzle attached to each individual electromagnetic transducer. The Venturi forces brought about by the escape of air from the space between the recording surface and the pole face surface positions the electromagnetic head out of contact with the recording surface at a distance dependent primarily upon the air pressure. The above described prior art systems are typical of most of the prior art information storage devices since it is a standard practice to move the magnetically sensitive medium in a first plane only and the electromagnetic transducer in a second plane generally perpendicular to the first plane until a predetermined precise gap is provided between the medium and the transducer resulting in the movement of at least two elements, and sometimes more, depending upon the structure used for mounting the electromagnetic transducer.-

Accordingly, it is an object of the present invention to provide an improved information storage device which is small, lightweight and has only one moving part.

A further object of the present invention is to provide an information storage device having increased memory capacity, environmental capability and higher reliability.

A still further object of the present invention is to provide an improved storage unit having at least one rigidly mounted electromagnetic transducer and a' movable information storage drum arranged to move relative to the transducer to accurately maintain and easily produce a precise gap between the pole piece surfaces of the transducer and the magnetic surface of the information storage drum.-

Briefly, the improved information storage device of the present invention comprises a stationary cylindrical support structure having at least one bore containing a rigidly bonded electromagnetic transducer assembly, an information storage drum having a coating of a magnetically sensitive material supported within the support structure to provide a precise, predetermined gap between the inner surface of support structure and the magnetically sensitive coating of the drum, and an electric motor having a rotor portion secured to the inner surface of the drum and a stator portion rigidly supported within the drum adjacent to the rotor.

Other advantages of the invention will herein become more fully apparent from the following description of the drawings which illustrate a preferred embodiment thereof, and in which:

FIGURE 1 is an enlarged perspective view of one embodiment of an improved information storage device provided in accordance with the .present invention and having a portion of the housing, magnetic drum and support structure cut away to illustrate the relative positioning of the various elements;

FIG. 2 is a longitudinal median sectional view of the support structure showing one of the bores for the ClCC? tromagnetic transducer assemblies;

FIG. 3 is an enlarged plan view of the bore shown in FIG. 3; and

FIG. 4 is an enlarged perspective view of the electromagnetic transducer assembly having the encapsulating material shown in broken lines to illustrate the ferrite core and the coil.

Referring to FIG. 1, while the primary structural elements of this embodiment will hereinafter be described, this description is included merely to facilitate an understanding of the invention, since the invention may be utilized in other embodiments of information storage systems without varying from the scope of the invention.

The primary structural elements of the information storage device of FIG. 1 are a housing and suitable electrical connectors and pressure fittings, a rotatable information storage drum 12 having a magnetically sensitive coating, an electric motor 14 coupled to the drum 12 to produce rotation thereof in response to a specific stimulus, a support means for the drum which will support the drum during operation to maintain it free for rotation and at a specific distance from at least one electromagnetic transducer assembly 16 which is rigidly supported by a support structure 18.

The drum 12 is cylindrically shaped, with both ends open and of a material such as aluminum and includes a hollow wall 19 of a magnetically sensitive material of increased hardness and improved coercivity and retentivity such as the one of the cobalt phosphorus alloys. The hollow wall 19 may be a single continuous piece; however, in the presently preferred embodiment it includes an outer member 20 coated with a layer of the magnetically sensitive material and an inner surface having a relatively thin portion 24 and a pair of flange portions 26 on both ends and of a width greater than said thin portion 24 to provide a thrust surface on the ends of the drum. The drum 12 is journalled within the cylindrical cavity of the support structure 18 and is supported radially free from an inner surface 28 of the structure during operation by a thin layer of hydrodynamic lubrication. This thin layer of lubrication is typically a layer of gas such as air which is maintained between the two surfaces during rotation by the fundamental principles of hydrodynamic gas bearings. A pair of thrust plates 30 are attached to a rigid shaft 32 which extends through the drum cavity so that each of them is in juxtaposition to a different one of the thrust surfaces or ends of the drum. The plates include a plurality of hydrodynamic bearings each of an arcuate shape to develop a pressure gradient during rotation of the drum which has a magnitude sufficient to axially support the drum free of the plates.

The electric motor 14 shown in FIG. 1 is a conventional induction motor of the inside-out type which includes a rotor 34 rigidly attached to the inside surface of drum 12 and a stator 36 mounted to the shaft 32 at a position adjacent to .the rot-or 34 so that by applying electrical signals to the stator field Winding magnetic torque can be developed in the rotor windings sufiicient to rotate the rotor and drum.

Referring to FIGS. 2 and 3, in addition to FIG. 1, the support structure 18 is cylindrically shaped, of a material such as aluminum, and includes at least one bore 38 extending from an outer or first surface 40 to the inner or second surface 28. The bore 38 includes a portion 42 beginning at the outer surface 40 having a fiat end wall 44 and an opening or aperture 46 beginning at the inner surface 28 and opening into the cylindrical portion 42. Typically, the opening has a rectangular cross section and is positioned centrally of the end wall 44 with its longitudinal axis perpendicular with the axis of rotation of the drum. While the portion 42 has been shown to be cylindrical, this shape is not critical since it may be of many different shapes within the teaching of the invention.

Referring to FIG. 4 the electromagnetic transducer assembly includes a pole piece or magnetic core 50 of a material such as a soft magnetic ferrite of a width less than the diameter of the bore 38. The core comprises two matched U-shaped core halves bonded together at one end and at the other end bonded to a shim 52 of low permeability of nonmagnetic material such as silver. The core contains stepped or notched shoulder portions 54 on both corners of the surface containing the silver shim to provide a police piece portion 56 of substantially the same dimensions as the rectangular opening 46. Wound around the two core halves is a coil 58 which may be typically wound from a single conductor 60 and having a center top 62 if desired for coupling to a push pull amplifier (not shown).

To assemble the support structure 18 and electromagnetic transducer assembly 16, the transducer assembly 16 may be encapsulated or enclosed in an enclosure 59 of a material such as epoxy having a content of aluminum oxide such as 72.5% aluminum oxide by weight which is high enough to give the assembly a thermal coefiicient of expansion substantially similar to that of the support structure. After the epoxy has cured, the assembly 16 is inserted into the bore 38 until the shoulder 54 of the core 50 is in contcat with the end wall 44 and the exposed surface of the projected portion 56 is substantially flush with the inner surface 28 of the support structure 18; thereafter, the transducer assembly 16 is rigidly bonded in the bore 38 by an epoxy such as that described above for encapsulation. While it has been found desirable in the preferred embodiment of the present invention to encapsulate the assembly 16 with a material whose thermal coefficient of expansion is substantially similar to that of the support structure 18, other means, such as the proper choice of materials for the assembly 18 may be utilized. After each of the transducer assemblies has been so positioned, the inner surface 28 and each of the pole piece surfaces projecting therefrom are simultaneously ground and honed with a conventional high precision grinding and honing machine until their roundness and finish is compatible with the drum 12. Thus, when the unit is in operation and the drum is journalled within the support structure by hydrodynamic lubrication, a precise space is provided between each of the pole piece surfaces and the magnetically sensitive surface of the drum and this spacing is maintained as long as the hydrodynamic lubrication is present since the only moving element is the storage drum which is being supported by the film of air.

While one embodiment of this invention has been herein illustrated, it should be appreciated by those skilled in the art that variations of the disclosed arrangement both as to its details and to the organization of such details may be made without departing from the spirit and scope thereof. Accordingly, it is intended that the foregoing disclosure and showings made in the drawings may be considered as illustrative of the principles of this invention and not construed in a limiting sense.

What is claimed is:

1. An information storage device comprising:

(1) a rotatable information storage drum including a magnetically sensitive material;

(2) a support structure circumscribing said drum;

(3) at least one electromagnetic transducer assembly having a thermal coefiicient of expansion substantially similar to that of said support structure and rigidly supported, in and by said structure in juxtaposition with said magnetically sensitive material;

(4) a support means coacting with said drum to provide a precise gap between said transducer assembly and the periphery of said drum; and

(5) rotation producing means coacting with said drum to produce rotation thereof in response to predetermined controllable electrical signals.

2. An information storage device as in claim 1 wherein said support means includes a cylindrical structure having an outer periphery and an inner periphery comprising:

(1) opening means in said support structure having a circular wall extending from said outer periphery toward said inner periphery and culminating in an end wall with aperture means therein extending to said inner periphery; and

(2) a stepped portion on said transducer assembly to provide a land for abutment against said end wall.

3. An information storage device comprising:

(1) a rotatable information storage drum including a magnetically sensitive material;

(2) a support structure circumscribing said drum and of a first material;

' (3) at least one electromagnetic transducer assembly of a second material having a thermal coefficient of expansion substantially similar to that of the material of said support structure and rigidly supported by said structure in juxtaposition with said magnetically sensitive material;

(4) a support means coacting with said drum to provide a precise gap between said transducer assembly and the periphery of said drum; and

(5) rotation producing means coacting with said drum to produce rotation thereof in response to predetermined controllable electrical signals.

4. An information storage device comprising:

(1) a rotatable information storage drum including a peripherial layer of magnetically sensitive material;

(2) a support structure circumscribing said drum;

(3) a plurality of electromagnetic transducer assemblies having a thermal coeflicient of expansion substantially similar to that of said support structure and rigidly supported by said structure in juxtaposition with said peripherial layer;

(4) support means coacting with said drum to provide a precise gap between said transducer assemblies and said peripherial layer; and

(5) rotation producing means coacting with said drum to provide rotation thereof in response to predetermined controllable electrical signals.

5. An information storage device comprising:

( 1) housing;

(2) a rotatable information storage drum including a peripherial layer of a magnetically sensitive material;

(3) a support structure of a first material supported within said housing and circumscribing said drum; (4) at least one electromagnetic transducer assembly adapted to be magnetically coupled to said peripherial layer, said assembly being rigidly supported by said support structure and including an encapsulation portion of a second material having a thermal coeflicient of expansion substantially similar to that of said first material;

(5) support means coacting with said drum to provide a precise gap between said transducer assembly and said peripherial layer; and

(6) rotation producing means coacting with said drum to produce rotation thereof in response to predetermined controllable electrical signals.

6. An information storage device comprising:

(1) a housing;

(2) a rotatable information storage drum including a peripherial layer of magnetically sensitive material;

(3) a cylindrical support structure supported in said housing circumscribing said drum, said structure being of a first material and having a plurality of circular bores extending from a first surface and terminating in a rectangular opening in a second surface in juxtaposition with said peripherial layer;

(4) a plurality of electromagnetic transducer assemblies each adapted to be magnetically coupled to said peripherial layer and including a core having a protruding portion with an elongated exposed surface, a coil of electrical conductors circumscribing said core, and an enclosure encapsulating a portion of said core and said coil of a material having a thermal coefficient of expansion similar to that of the first material, each of said assemblies being rigidly bonded in a different one of said bores with the protruding portion inserted into said rectangular opening with said elongated exposed surface substantially flush with said second surface;

(5) a means coacting with said drum to provide a precise gap between said transducer assemblies and said peripherial layer; and

(6) rotation producing means coacting with said drum to produce rotation thereof in response to controllable electrical signals.

References Cited UNITED STATES PATENTS 3,133,159 5/1964 Johnson 179---100 3,180,715 4/1965 Simon 22-194 3,270,328 8/1966 McCreary 340 174.1

BERNARD KONICK, Primary Examiner. R. SNIDER, A. I. NEUSTADT, Assistant Examiners. 

